1. Field of the Invention
The invention is related to the field of charging in communication networks, and in particular, to a centralized charging system for offline charging and online charging in communication networks, such as 3GPP/3GPP2 networks.
2. Statement of the Problem
Service providers typically provide numerous voice and/or data services to subscribers using one or more wireline and/or wireless communication networks. Exemplary services include cellular telephony, access to the Internet, gaining, broadcasting or multicasting of audio, video, and multimedia programming, etc. Mobile devices, such as cell phones, personal data assistants, smart phones, pagers, text messaging devices, global positioning system (GPS) devices, network interface cards, notebook computers, and desktop computers, may access the services provided by the communication networks over an air interface with one or more base stations. Communication between the mobile devices and base stations are governed by various standards and/or protocols, such as the standards and protocols defined by the 3rd Generation Partnership Project (3GPP, 3GPP2).
The service providers use offline and online billing functions to keep track of the charges incurred by each device for using the various services. The 3GPP/3GPP2 standards groups have defined a set of specifications that may be used to implement online charging systems and offline charging systems to cover charging in the various network domains (e.g., a circuit switching network domain, a packet switching network domain, and/or a wireless domain), IP multimedia subsystems, and emerging 3G/OMA application services.
Online charging is generally defined as a charging mechanism where charging information can affect, in real-time, the service rendered, and therefore a direct interaction of the charging mechanism with session/service control is needed. In online charging, charging information for network resource usage is collected concurrently with the resource usage. However, authorization for the network resource usage must be obtained by the network prior to the actual resource usage. The network elements in a communication network, such as a Call Session Control Function (Proxy, Serving, Interrogate) or an application server (AS) in an IMS network, include Charging Trigger Functions (CTF). For online charging, the CTF triggers on charging events, collects charging information pertaining to the charging events, and assembles the charging information into matching charging events. The CTF then transmits accounting messages to the Online Charging System (OCS) in order to obtain authorization for the charging event/network resource usage requested by the user. The CTF delays the actual resource usage until permission has been granted by the OCS. When a granted quota of service units is obtained from the OCS, the CTF performs budget control during the resource usage. The CTF enforces termination of the end user's resource usage when permission by the OCS is not granted or expires.
Offline charging is generally defined as a charging mechanism where charging information does not affect, in real-time, the service rendered. In offline charging, charging information for network resource usage is collected concurrently with resource usage. The CTF triggers on charging events, collects charging information pertaining to the charging events, and assembles the charging information into matching charging events. The CTF then transmits accounting messages to a Charging Data Function (CDF).
According to the present 3GPP specifications (TS 32.240), the CTF imbedded in each network element includes two parts. One part of the CTF is the accounting metrics collection function. The accounting metrics collection function provides metrics that identify the user and the user's consumption of network resources and/or services in real-time. The accounting metrics collection function is considered dependent on the network element. From the charging mechanism perspective, online charging and offline charging have the same collection function, and are transparent to the accounting metrics collection function. Thus, the accounting metrics collection function is considered as charging mechanism independent.
Another part of the CTF is the accounting data forwarding function. The charging information received by the accounting data forwarding function from the accounting metrics collection function, and the relevant charging events, are specific to each type of network element. The overall functionality of receiving, assembling, and forwarding the charging information may be considered generic. Thus, the accounting data forwarding function is considered the independent from the network element.
According to the present 3GPP specifications, the CTF is a mandatory, integrated component in all network elements that provide online/offline charging functionality. This means that each network/subsystem/service element will have its own CTF to implement both the accounting metrics collection function and the accounting data forwarding function in its CTF. One problem with the present offline/online charging mechanisms is that when a network operator wants to enhance the accounting data forwarding functionality, each network element will need to be upgraded (software modification and upgrade). These upgrades can be time consuming and complex, especially in communication networks having a significant number of network elements.
Further, when an accounting data forwarding function is implemented in the CTF of each network element, the network element needs to maintain a charging mechanism profile for each user, and needs to have different data forwarding treatment for online charging and offline charging. Because the specific call treatment for offline charging and online charging are different, the accounting data forwarding function may overload the network element. Thus, many service providers opt to implement offline charging data forwarding, but do not implement advanced online charging accounting data forwarding with budget control. These service providers are unfortunately missing out on the services and revenue generated from online charging.